1. Field of the Invention
The present invention pertains to rigid cellular foams characterized by carbodiimide linkages. More particularly, the present invention relates to the preparation of rigid cellular foams characterized by carbodiimide linkages by the catalytic condensation of an organic polyisocyanate. Even more particularly, the present invention concerns the preparation of rigid cellular foams characterized by carbodiimide linkages from the catalytic condensation of acid-modified toluene diisocyanate.
2. Prior Art
In copending U.S. patent application Ser. No. entitled "Urethane-Modified Carbodiimide-Isocyanurate Foams Prepared From TDI-Rich Isocyanates", filed the disclosure of which is hereby incorporated by reference, there is discussed the problems of using "pure or distilled" toluene diisocyanate, i.e., a 99% pure 80:20 weight mixture of 2,4- and 2,6-toluene diisocyanate, in the preparation of rigid cellular foams of the type under consideration herein. Furthermore, the referred to application teaches two methods for using pure toluene diisocyanate in the preparation of these foams. One such method disclosed therewithin comprises a two-step process wherein an active-hydrogen containing compound is reacted, in situ, with excess pure toluene diisocyanate, generally, in the presence of a urethane catalyst. This is followed by the catalytic condensation of the resulting product in the presence of a co-catalyst system. comprising a carbodiimide catalyst and an isocyanate trimerization catalyst. The use of a two-step process is viable, but if a one-step or one-shot process could be employed many inherent processing advantages immediately arise.
The other method disclosed in the referred to application teaches the use of an isocyanate-terminated quasi-prepolymer prepared from an excess amount of pure toluene diisocyanate to produce the present foams. Although this method is quite efficacious, it has been found that when a reactive polyol is used to prepare the quasi-prepolymer, the quasi-prepolymers exhibit only limited storage stability. Thus, it would be advantageous to overcome this problem by providing quasi-prepolymers which are storage stable.
The present invention overcomes both of the herein considered problems.